The trim is pulled out after the window and rubber are out of the car. It bends VERY easily and looks like crap when it does.
IIRC I did something "cheap" and used a couple of bits of high density foam (you could also make little "rolls" of electrical tape) and use it to hold the wire in the moulding (in the water channel). On my 210 I just stashed the antenna on top of a steel part underneath the package shelf. I get decent reception and it is pretty stealth. -j.